As a fixing device used in image forming apparatus such as electro-photographic copying machines, printers, facsimiles, there is a fixing device which heats, pressurizes and fixes a toner image by inserting a sheet paper between a pair of rollers comprising a heat roller and a pressure roller or similar belts. In this heating type fixing device, in order to maintain heat rollers at a constant temperature able to fix images, surface temperature of the heat roller is detected by a heat sensor and a heat source is controlled by turning it ON/OFF according to the detected result.
In recent years, a non-contact type temperature sensor is used, which detects temperature without contacting members to be heated such as heat rollers, fixing belts like a thermopile type infrared temperature sensor. This temperature sensor assures the long life of heat rollers without injuring the surfaces of heating members.
For this non-contact type infrared temperature sensor, it is necessary to remove dirt adhered to the lens surface of the sensor in order to obtain the high detecting accuracy. Therefore, at the time when a fixing device was pulled out from the main body of an image forming apparatus for the service maintenance, the jam process or exchange of the fixing device at the end of its service life, it was so far required to wipe off dirt on the temperature sensor installed in the main body by a service man. Further, there is a device to wipe off dirt on a filter by reciprocating a cleaner of the front surface of the temperature sensor filter.
However, in the case of a conventional fixing device wherein its temperature sensor is cleaned by a service man by wiping off the sensor at the time of checking, the workability of a service man will drop. Further, in the case of a conventional fixing device wherein a cleaner or filter is moved, a moving mechanism becomes necessary, the device will be complicated and the downsizing of the apparatus is checked.
So, in the field of a fixing device to heat and fix images, it is desirable to develop a fixing device of an image forming apparatus, capable of easily removing dirt adhered on the surface of a thermopile type temperature sensor to detect surface temperature of units to be heated, promoting the detecting accuracy of the temperature sensor, obtaining high image quality by precisely controlling temperatures of heating members and furthermore, without impairing the maintenance efficiency by promoting the fixing performance, and achieving downsizing of an image forming apparatus simple in structure.